The instant invention relates to devices for sensing fluid flow rates and more particularly to a device which is operative for sensing very low fluid flow rates in relatively small diameter conduits.
While a wide variety of fluid flow measuring devices have been heretofore available, most of them have been ineffective for measuring very low fluid flow rates in relatively small diameter conduits and pipe sections, such as those having diameters of less than approximately two inches. In this regard, heretofore paddle-wheel-type flow measuring devices have been effectively used for measuring fluid flow rates in many low flow applications. However, it has been found that, while paddle-wheel-type flow measuring devices can be effectively used for measuring relatively low fluid flow rates in relatively large diameter conduits and pipe sections, they generally loose their effectiveness when they are made in miniaturized constructions for use in measuring fluid flow rates in relatively small diameter conduits and pipe sections. This is primarily because as the overall diameter of a paddle-wheel is decreased, the amount of torque which is applied to the paddle-wheel by a fluid as it contacts the paddles or paddle elements thereof is decreased correspondingly, whereas the frictional resistance to the rotation of the paddle-wheel caused by the assembly in which it is mounted remains substantially the same. Accordingly, as the diameter of a paddle-wheel is reduced, the frictional resistance to the rotation of the wheel becomes increasingly significant and, in fact, it has been found that in some instances this frictional resistance can prevent relatively small diameter paddle-wheels from rotating under very low flow conditions and that under other conditions it can cause paddle-wheel-type flow measuring devices to produce erroneous flow readings.
Flow measuring devices representing the closest prior art to the instant invention of which the applicant is aware are disclosed in the U.S. patents to COLEMAN U.S. Pat. No. 1,579,280; DENISON et al U.S. Pat. No. 4,101,874; POUNDER U.S. Pat. No. 4,173,144; ONODA U.S. Pat. No. 4,265,127; LAVIANO et al U.S. Pat. No. 4,379,411; and POUNDER et al U.S. Pat. No. 4,440,030. Of these devices, the ones disclosed in the U.S. Pat. Nos. to POUNDER 4,173,144 and POUNDER et al 4,440,030 are believed to be the most pertinent to the instant invention since they address the problem of measuring very low fluid flow rates. However, since they do not address this problem in the manner of the instant invention and since they do not anticipate the novel structural features of the device of the instant invention, even these references are believed to be of only general interest.
The instant invention provides a novel flow measuring device which is operative for measuring relatively low fluid flow rates in conduits, even conduits having relatively small diameters or sectional dimensions, such as those having sectional dimensions of less than approximately two inches. More specifically, the flow measuring device of the instant invention comprises a housing having an open interior area, a paddle-wheel mounted in the housing and means for sensing the rate of rotation of the paddle-wheel in the housing. The paddle-wheel, which has a central axis, comprises a plurality of paddle elements which extend outwardly relative to the central axis. Further, the paddle-wheel is mounted in the open interior area of the housing so that it is rotatable about its axis and the housing is formed with inlet and outlet passages which extend between the open interior area and the exterior of the housing. The inlet passage of the housing is oriented so that when a fluid which is flowing in generally perpendicular relation to the axis of the paddle-wheel passes through the inlet passage into the open interior area, it impinges directly on the portions of the paddle-wheel which are adjacent a first end thereof but not directly on the portions of the paddle-wheel which are adjacent the axially opposite second end thereof, and the outlet passage is oriented to receive fluid directly from portions of the paddle-wheel which are adjacent the second end thereof but not directly from portions of the paddle-wheel which are adjacent the first end thereof. Accordingly, when a fluid passes through the inlet passage into the open interior area, it impinges directly on the first end portion of the paddle-wheel and it causes the paddle-wheel to rotate about its axis. However, since the fluid can not pass directly from the first end portion of the paddle-wheel to the outlet passage, it circulates with the paddle-wheel in the housing until it is reoriented adjacent the second end portion of the paddle-wheel, whereupon it can escape through the outlet passage as the paddle-wheel rotates further. This internal circulation of fluid in the housing around the paddle-wheel causes the rotational forces which are applied to the paddle-wheel to be increased so that proportionally the effects of the frictional resistance from the assembly in which the paddle-wheel is mounted are diminished. In the preferred embodiment of the device of the instant invention the inlet and outlet passages are laterally offset with respect to each other to assure that fluid from the inlet passage impinges on the first end portion of the paddle-wheel but not on the second end portion thereof and to assure that the outlet passage is positioned to receive fluid from the second end portion of the paddle-wheel but not from the first end portion thereof. Further, in the preferred embodiment the housing is constructed so that when fluid passes from the inlet passage through the interior area to the outlet passage, it circulates at least an entire revolution around the axis of the paddle-wheel and the housing preferably confines the fluid in the interior area so that a substantial portion of the fluid rotates with the paddle-wheel. In one embodiment of the device, the housing is constructed so that the open interior area has a substantially circular sectional configuration and the paddle-wheel is mounted so that the axis thereof is in substantially diametric relation in the open interior area. In this embodiment of the device, the housing comprises a longitudinally extending sidewall portion which defines the circular periphery of the interior area and an end wall which defines an end of the interior area. Further, a slot is formed in the housing which extends through the end wall and the adjacent end portions of the side wall portion in substantially diametric relation to the circular interior area, the slot preferably being disposed at an angle of between approximately 60.degree. and 80.degree. with respect to the axis of the paddle-wheel. For use of this embodiment of the device, it is preferrably mounted in a pipe section so that the housing extends inwardly a distance into the interior of the pipe section from a peripheral side wall thereof and the paddle-wheel is preferably oriented so that the axis thereof is substantially perpendicular to the axis of the pipe section. It has been found that when the device of the instant invention is constructed and mounted in this manner it can be effectively embodied in miniaturized constructions and it can be utilized for measuring relatively low flow rates in relatively small diameter pipes and conduits. In particular, when the device is constructed and mounted in the manner hereinabove set forth, and it is subjected to a flow of fluid, a substantial portion of the fluid circulates around the paddle-wheel in the interior area of the housing so that the rotational forces applied to the paddle-wheel are substantially increased. This allows the paddle-wheel of the device to effectively overcome the frictional resistance caused by the assembly in which it is mounted so that the device can be effectively utilized for measuring relatively low flow rates in even small diameter conduits.
Accordingly, it is a primary object of the instant invention to provide an effective device for measuring relatively low rates of fluid flow.
Another object of the instant invention is to provide an effective device which can be utilized for measuring low fluid flow rates in relatively small diameter pipe sections and conduits.
Another object of the instant invention is to provide a flow measuring device comprising a housing and a paddle-wheel mounted in the housing, wherein fluid passing through the housing circulates around the paddle-wheel to apply increased rotational forces thereto.
Other objects, features and advantages of the invention shall become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawings.